A 20 long would give you a ton of room to make an epic scape, but anything larger than 5 gallons is fine. I would personally opt for a 10 gallon. It is large enough to give the betta TONS of space, but small enough to make a single piece of driftwood look really awesome lol. Bettas thrive in as natural of a tank as possible. If you want the ultimate betta setup, match it to their natural habitat as closely as possible. If it were me, I would do
10 gallon tank
No filter
Heater, 78 degrees F
Natural sand substrate (pool filter sand is great)
Indian almond leaves
A large piece of driftwood as a centerpiece piece of decor
Amazon swords, water sprite, dwarf sag, Italian vals, a variety of anubias, lots of floating plants, bamboo, Anacharis, red ludwigia
Betta
2 nerite snails
Again, 10 gallons is a great size. I have a piece of driftwood that looks awesome in a 10 gallon, it spans the entire length and is a real centerpiece. In a large 55 gallon tank it looks nice as a decorative touch. In a 20 gallon though it just looks off. Kind of like “either commit and be the centerpiece, or be smaller and just a subtle decorative touch. Just pick one!”
Here it is to show you what I mean.
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